High-frequency voltage controlled oscillators ("VCOs) are widely used in integrated circuits, ranging from clock recovery in high data-rate optical communications to frequency synthesizer in wireless communications. Frequency tuning for these VCOs can be achieved with varactor diodes. However, the frequency tuning range using this approach is limited by low supply voltages on integrated circuits and maximum variable capacitance available to varactors at high frequencies when inductors are used. Other frequency turning approaches include varying the current in the resonator of the oscillator to alter effective capacitance or varying the relative weighing between two different LC (Inductor-Capacitor) resonators. These techniques are not adequate for tuning frequency.